When conditions are just right - very cold and very still air - a dense fog can form long, needle-like crystals of rime (not ice); the super-cooled water remains liquid below the usual freezing point and doesn't freeze until the droplets contact a solid surface. "Rime" is similar to that white stuff that needed to be cleared out of older freezers. Conditions for a pogonip may only last hours but may last for days.

Relatively common in western Nevada, the local Paiute lived in sagebrush huts and feared the coming of the pogonip. Breathing the frozen air would cause sore throats at best, a difficulty in breathing, and a ripe environment for pneumonia - the white death.

This photo was taken outside Fernley, Nevada about this time of year; the crystals on the trees were 2" and longer in length.

It's a good idea to wear a mask when outside for any length of time under these conditions.

One might speculate as to whether DT wore a mask when wandering around this copse ...

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